A conventional in-vehicle navigation system displays, on a road map, characters such as: address names or administrative district names including names of prefectures, cities, and towns; facility names including park names; and road names. Users can thus acquire information on names to specify an area where the vehicle runs, peripheral facilities, and relevant roads. Herein, display positions of such information on names are predetermined in road map data; thus, each name is displayed at a corresponding predetermined position on a road map.
The address names or facility names are generally necessary for a user to confirm a place the vehicle runs. A user determines an approximate route to a desired destination, and thereby drives a vehicle. The names of relevant roads are therefore more important than those of addresses or facilities for such a user. This is because the user determines one by one which road to run along the approximate route based on road names in many cases.
However, the necessity that the user understands all the road names displayed in the navigation system is low. That is, the user can drive the vehicle along the previously determined route as long as the user can know the road subsequent to the present road the vehicle is running.